1. Field of the Invention
The present invention relates to a counter steer detecting method, and more particularly to a method of detecting counter steer accurately and early.
2. Description of the Related Art
The turning performance of a vehicle can be improved by providing a differential for controlling the difference in torque between right and left drive wheels. However, when one of the right and left drive wheels slips, torque distribution to the drive wheels by the differential is not performed. Accordingly, it is necessary to control the torque distribution according to a running condition of the vehicle. In a four-wheel drive vehicle, the difference in torque between front and rear wheels is controlled to improve both the turning performance and the running stability of the vehicle.
In general, when the differential action of a differential is limited, the running stability is improved, whereas when the differential action is not limited, the turning performance is improved. In the case that counter steer occurs in drift running or the like, the differential action is locked to thereby improve the running stability. Accordingly, the determination of counter steer is required to properly operate the differential and thereby to perform optimum torque distribution.
Conventional counter steer determining methods are disclosed in Japanese Patent NoS. 4-201726 and 2002-96652. The method disclosed in Japanese Patent No. 4-201726 is that the counter steer is determined when the direction of turn of a vehicle obtained from a lateral acceleration (which will be hereinafter referred to also as lateral G) detected by lateral G detecting means is different from the direction of steer detected by steering angle detecting means, that is, when the sign of the lateral G is different from the sign of the steering angle. On the other hand, the method disclosed in Japanese Patent No. 2002-96652 is that the counter steer is detected according to the magnitude of an actual lateral G detected by a lateral G sensor and the magnitude of a calculated lateral G.
The method disclosed in Japanese Patent NO. 4-201726 has the following problems. First, until the direction of steer becomes opposite to the direction of turn of the vehicle, the counter steer cannot be detected, so that the detection of the counter steer is delayed. Secondly, the sign of the steering angle becomes momentarily different from the sign of the lateral G because of delay characteristics of the vehicle and the lateral G sensor in slalom running or the like, and the counter steer is improperly determined in spite of the above case where no counter steer occurs.
The method disclosed in Japanese Patent No. 2002-96652 has the following problems. First, since the counter steer is detected according to the magnitude of the actual lateral G detected by the lateral G sensor and the magnitude of the calculated lateral G, it is difficult to determine the correlation between the counter steer and the magnitudes of the actual lateral G and the calculated lateral G, so that accurate detection of the counter steer is difficult. Secondly, until the direction of steer becomes opposite to the direction of turn of the vehicle, the counter steer cannot be detected, so that the detection of the counter steer is delayed.